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How to highlight the first parameter sent to a macro using only a variable parameter

I am trying to get the first actual parameter sent to a variable macro. This is what I tried and which does not work in VS2010:

#define FIRST_ARG(N, ...) N
#define MY_MACRO(...) decltype(FIRST_ARG(__VA_ARGS__))

When I look at the output of the preprocessor, I see that it FIRST_ARGreturns the entire list of arguments sent to MY_MACRO...

On the other hand, when I try:

FIRST_ARG(1,2,3)

it expands to 1 as intended.

It seems that this is somehow the opposite of the problem solved by the infamous concat macros of two levels. I know that "macro parameters are fully expanded before inserting into the macro body", but this does not seem to help me, because I do not understand what this means in context ... and__VA_ARGS__

, __VA_ARGS__ N . , .

+2
1

Visual ++. , , . :

#define FIRST_ARG_(N, ...) N
#define FIRST_ARG(args) FIRST_ARG_ args
#define MY_MACRO(...) decltype(FIRST_ARG((__VA_ARGS__)))

MY_MACRO(x, y, z)

:

decltype(x)
+6

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